Color inkjet printers have become popular for printing on media when precise printing of color images is needed. For instance, such printers have become popular for printing color image files generated using digital cameras. Within such printers, accurate color printing can be ensured by using two inkjet print cartridges, each having corresponding color inks. One print cartridge, for instance, may have the colors cyan, magenta, and yellow, whereas the other print cartridge may have the colors light cyan, light magenta, and light yellow.
For accurate color printing, the two inkjet print cartridges should be color balanced with one another. Manufacturing, process, and formulation variations can alter the nominal drop volumes of the print cartridges, upsetting the balance between the two print cartridges, and thus causing the reproduced colors to shift in hue. Drop volume compensation is one process used to color balance the two print cartridges. Drop volume compensation determines the change in saturation level needed for the colors of one of the print cartridges to match the corresponding colors of the other print cartridge. Accurate color printing can then be accomplished more easily. The saturation levels themselves are dependent on the relative drop volumes of ink ejected from the print cartridges, hence the phrase drop volume compensation.
A reflectance sensor measures the optical density of a pattern printed with ink of unknown drop volume at a specific saturation level from an inkjet print cartridge. Within the same type of printer, different kinds of reflectance sensors from different manufacturers may be used. These different reflectance sensors may measure saturation levels differently, affecting the drop volume compensation, and hence the color balancing of the inkjet print cartridges. For this and other reasons, therefore, there is a need for the present invention.
At least some embodiments of the invention disclose drop volume compensation that is at least substantially invariant to the illuminate of the reflectance sensor being used. A method of one embodiment first prints a pattern of a predetermined mixture of colorants that results in at least a substantially identical response from each of a number of reflectance sensors that have different illuminate spectral emission profiles. Drop volume compensation is then performed to color balance a first colorant source to a second colorant source, utilizing the predetermined mixture of colorants and one of the reflectance sensors. The drop volume compensation is at least substantially invariant to the reflectance sensor utilized.